An important component of any system designed to produce and pass RF signals such as, for example, cellular phones and other wireless communication equipment systems, is the power amplifier which amplifies the signals associated with the system. These amplifiers typically include one or more delay elements which, preferably have a uniform, temperature stable, and fixed amount of insertion delay and linear phase over a predetermined frequency range.
A “feedforward correction” scheme has to date been used to linearize power amplifiers. It employs two loops, the main amplifier-carrier cancellation loop and the error amplifier-intermodulation cancellation loop. The delay of the amplifiers in both loops needs to be well matched to achieve cancellation over a broad bandwidth.
Delay modules most commonly incorporate filters for filtering and delaying the RF signal passing therethrough and circuits associated therewith for equalizing the delay across the passband of the filter.
The circuits for equalizing the delay across the passband of the filter most commonly have incorporated couplers and discrete, lumped resonator L-C components of the type disclosed in, for example, U.S. Pat. No. 3,277,405 to Cohn and U.S. Pat. No. 6,317,013 to Hershtig.